(1) Field of the Invention
This invention is concerned with shoe stiffeners, especially stiffeners for use in stiffening the toe or heel end portions of a shoe upper. The term "shoe" is used herein generically to denote outer footwear generally, whether ready for wear or in the course of manufacture.
(2) Description of the Prior Art
In the manufacture of shoes it is a common practice to include in the upper assembly stiffeners in toe and heel regions adhered to the outer integument of the upper to assist in retaining the toe and heel end portions of the shoe in a desired configuration. The stiffeners are commonly adhered to the outer integument of the upper using a suitable adhesive, for example a hot melt adhesive or a rubber latex. One type of shoe stiffener extensively used in shoe-making comprises a textile fabric, for example a non-woven textile fabric, impregnated with a polymer dispersion and subsequently dried to provide the desired stiffness (see for example United Kingdom Patent Specification No. 935001). Such materials are preferably activated by heat to render them malleable for lasting; alternatively they may be activated for lasting by a solvent treatment but the use of solvents is not attractive to some shoe manufacturers even though the stiffeners, after solvent activation, may have better creep resistance and greater stiffness than the equivalent commercially available heat-activated materials. Another type of stiffener widely used comprises a textile fabric impregnated with a polymer solution which is then dried, to provide the desired stiffness: such solution-impregnated stiffeners have in the past generally been stiffer and more creep-resistant than commercially available emulsion-impregnated materials of similar weight. Some shoe manufacturers in the manufacture of certain types of shoe prefer to stick the stiffeners to the shoe upper using latex adhesives e.g. rubber latex adhesive compositions or polyvinyl acetate latex adhesive compositions, while others prefer heat-activated adhesives. Most latex adhesives cannot satisfactorily be used to bond known stiffeners consisting of a textile fabric impregnated with polymer dispersion to the outer integument of a shoe upper.